Field of the Invention The invention relates to a honeycomb body having an axis along which it can conduct a flow of fluid through the honeycomb body, and the honeycomb body extends along the axis and it is delimited by two opposed ends.
The invention relates particularly to honeycomb bodies that are suitable for and intended as carrier bodies for catalytic converters, for instance in motor vehicle exhaust systems.
Honeycomb bodies that are formed of metal structures, in particular at least partially structured metal sheets, are described in Published International Application WO 89/07488 and in Published International Application WO 90/03220, corresponding to U.S. Pat. No. 5,135,794. In order to form such honeycomb bodies, metal sheets, including corrugated sheets, are disposed in layers and wound around an axis. In order to increase mechanical stability, the layers may be partially reinforced. The reinforcements need not extend over the entire length of a honeycomb body along its axis but rather may be limited to portions, in particular portions in the vicinity of ends of the honeycomb body.
In order to provide purposeful variation of the flow of a fluid, for instance exhaust gas from an internal combustion engine, through a honeycomb body, the sheets forming a honeycomb body may be provided with small structures. Turbulence that improves the contact of the fluid with the honeycomb body and thus reinforces a reaction effected by a catalyst on the honeycomb body in the fluid occur, for instance, at such structures. In Published International Application WO 90/08249, the metal sheets forming a honeycomb body are provided with microstructures which extend crosswise or at an angle relative to the flow direction of the fluid. Such microstructures include fluting, beads, bumps, or grooves. In Published International Application WO 91/01178, corresponding generally to co-pending U.S. application Ser. Nos. 711,564, filed May 30, 1991 and 900,836, filed Jun. 18, 1992, the metal sheets forming the honeycomb bodies are provided with openings, with which flow baffles are associated. Such flow baffles are capable of conducting partial streams of the fluid flowing through the honeycomb body through the openings and thus reduce boundary layer effects. Through the use of a systematic configuration of openings and flow baffles, the flow profile in the honeycomb body can additionally be made more uniform. In Published International Application WO 91/01807, corresponding generally to U.S. Pat. Nos. 5,045,403 and 5,130,208, corrugated metal sheets in the honeycomb body are provided with folded-over features, which form additional leading edges in the interior of the honeycomb body and likewise make it possible to suppress boundary layer effects.
In Published European Application No. 0 279 159 A1, corresponding to U.S. Pat. No. 4,845,073, a metal catalyst carrier body is formed of alternating layers of two differently corrugated metal sheets. A honeycomb body of that kind is distinguished by especially high mechanical strength. It is particularly well suited for applications that involve high thermal alternating strains.
Published International Application WO 89/10470 and Published International Application WO 89/10471 disclose honeycomb bodies formed of metal sheets, that are directly electrically heatable. Since conventional catalytic converters for use in the exhaust systems of internal combustion engines do not develop their effectiveness until reaching elevated temperatures, typically above approximately 300.degree. C., no catalytic reaction initially ensues at the onset of a flow of exhaust gas around a cold catalyst, so that the catalyst must first be preheated to an adequately high temperature. In order to speed up such preheating or even accomplish it before an engine is turned on, a metal honeycomb body can be heated directly electrically, by passing an electrical current through it. The electrical resistance of the honeycomb body may have to be adapted to the properties of the electrical power source which is available. In a honeycomb body for use in a motor vehicle, there must be a current path with a resistance on the order of magnitude of 0.1 Ohms for the electrical current to pass through. In order to attain that, the honeycomb body can be electrically subdivided in its cross-sectional area and/or its axial length by means of gaps and/or electrically insulating intermediate sheets. In Published International Application WO 90/12951, the strength of an electrically directly heatable honeycomb body can be increased by incorporating form-locking connections in the honeycomb body between sheets and ceramic intermediate sheets, with every two sheets enclosing one ceramic intermediate sheet. A form-locking connection is one which connects two elements together due to the shape of the elements themselves, as opposed to a force-locking connection, which locks the elements together by force external to the elements.
The information available from the prior art on the way in which to construct an electrically directly heatable honeycomb body, especially a honeycomb body for use as a carrier body for a catalytic converter in a motor vehicle exhaust system, does not in every case assure an adequately stable and mechanically loadable structure. Incorporating gaps and/or electrically insulating sheets, such as ceramic layers, may involve a sacrifice in terms of force-locking connections between various layers in the honeycomb body and thus may cause intolerable loosening of the mechanical structure of the honeycomb body.